Field of the Invention
The present invention relates to novel delaminated metallosilicate zeolite materials and methods of preparing such materials. More specifically, provided is a simple, surfactant-free, one-step synthesis for delaminating borosilicate layered zeolite precursors.
Description of the Related Art
Zeolites demonstrate extraordinary catalytic utility due to their well-defined catalytic active sites consisting of heteroatoms substituted within the zeolitic framework as well as shape selectivities. However, zeolites have been limited to microporous frameworks in the past, which has limited reactant substrates to small molecules. Incorporating greater accessibility into zeolite catalysts would be invaluable to expanding the scope of their catalysis to include larger and sterically more bulky substrate and product molecules, and has served as a lofty goal in the synthesis of this class of materials. Over the years, there have been many elegant enabling efforts towards this goal, including synthesis of extra-large pore zeolites, (see Davis, M. E. Chemistry-a European Journal 1997, 3, 1745 and Jiang, J.; Yu, J.; Corma, A. Angewandte Chemie-International Edition 2010, 49, 3120), delaminated layered zeolite precursor materials, (Corma, A.; Fornes, V.; Pergher, S. B.; Maesen, T. L. M.; Buglass, J. G. Nature 1998, 396, 353; Ogino, I.; Nigra, M. M.; Hwang, S.-J.; Ha, J.-M.; Rea, T.; Zones, S. I.; Katz, A. Journal of the American Chemical Society 2011, 133, 3288; Eilertsen, E. A.; Ogino, I.; Hwang, S.-J.; Rea, T.; Yeh, S.; Zones, S. I.; Katz, A. Chemistry of Materials 2011, 23, 5404; Ogino, I.; Eilertsen, E. A.; Hwang, S.-J.; Rea, T.; Xie, D.; Ouyang, X.; Zones, S. I.; Katz, A. Chemistry of Materials 2013; and Maheshwari, S.; Jordan, E.; Kumar, S.; Bates, F. S.; Penn, R. L.; Shantz, D. F.; Tsapatsis, M. Journal of the American Chemical Society 2008, 130, 1507), single-unit-cell zeolite nanosheets (see Choi, M.; Na, K.; Kim, J.; Sakamoto, Y.; Terasaki, O.; Ryoo, R. Nature 2009, 461, 246), hierachically nanoporous zeolitelike materials (Na, K.; Jo, C.; Kim, J.; Cho, K.; Jung, J.; Seo, Y.; Messinger, R. J.; Chmelka, B. F.; Ryoo, R. Science 2011, 333, 328) and self-pillared zeolite nanosheets (Zhang, X.; Liu, D.; Xu, D.; Asahina, S.; Cychosz, K. A.; Agrawal, K. V.; Al Wahedi, Y.; Bhan, A.; Al Hashimi, S.; Terasaki, O.; Thommes, M.; Tsapatsis, M. Science 2012, 336, 1684). Nevertheless, all of these approaches, while beautiful in their own right and highly successful for providing larger molecules with catalytic accessibility to zeolites, require an intricate self-assembly between organic surfactants and the inorganic zeolite framework. These surfactants are costly to synthesize and render the process of accessible zeolite synthesis less atom efficient, since they are typically irreversibly consumed (e.g. calcination) prior to use. An emerging approach for synthesis of accessible zeolitic structures that does not require organic surfactants includes synthesis of MCM-56 analogues, which consist of disordered sheets of zeolite layers, using mild acid treatment of the as-made
MWW layered zeolite precursors, which removes some of the structure-directing agent. Such materials, when substituted with metal heteroatoms, have shown catalytic activity using sterically bulky reactants, such as Ti-catalyzed epoxidation of cyclooctene using tertbutylhydroperoxide as oxidant; Al-catalyzed cracking of 1,3,5-triisopropylbenzene, and Sncatalyzed Baeyer-Villiger oxidation of 2-adamantanone (Wang, L.; Wang, Y.; Liu, Y.; Chen, L.; Cheng, S.; Gao, G.; He, M.; Wu, P. Microporous and Mesoporous Materials 2008, 113, 435; Wang, Y.; Liu, Y.; Wang, L.; Wu, H.; Li, X.; He, M.; Wu, P. Journal of Physical Chemistry C 2009, 113, 18753; and Liu, G.; Jiang, J.-G.; Yang, B.; Fang, X.; Xu, H.; Peng, H.; Xu, L.; Liu, Y.; Wu, P. Microporous and Mesoporous Materials 2013, 165, 210.) Another promising approach for synthesis of accessible zeolites is the transformation of three-dimensional UTL germanosilicate into a two-dimensional lamellar zeolite by Cejka et al., who demonstrated that layers are separated during hydrolysis of the double-four ring (D4R) bridging units by hydrolysis (Roth, W. J.; Shvets, O. V.; Shamzhy, M.; Chlubna, P.; Kubu, M.; Nachtigall, P.; Cejka, J. Journal of the American Chemical Society 2011, 133, 6130; and Chlubna, P.; Roth, W. J.; Greer, H. F.; Zhou, W.; Shvets, O.; Zukal, A.; Cejka, J.; Morris, R. E. Chemistry of Materials 2013, 25, 542.) This latter approach, while elegant, requires precursors to consist of D4R units in the space between layers, such that D4R removal via hydrolysis results in two-dimensional zeolite layers, and has only been synthetically demonstrated on zeolite UTL.
Borosilicate zeolites have historically been generally considered to be less useful for acid-catalyzed reactions because their intrinsically weak acidity can effectively catalyze reactions that require mild acidity (Millini, R.; Perego, G.; Bellussi, G. Topics in Catalysis 1999, 9, 13; Chen, C. Y., Zones, S. I., Hwang, S. J., Bull, L. M. In Recent Advances in the Science and Technology of Zeolites and Related Materials, Pts a-C; VanSteen, E., Claeys, M., Callanan, L. H., Eds. 2004; Vol. 154, p 1547; and Chen, C. Y., Zones, S. I. In 13th International Zeolite Conference; Galarneau, A., Di Renzo, F., Fujula, F., Vedrine, J., Eds.; Elsevier: Amsterdam, 2001, p paper 26.) However, borosilicate zeolites provide a unique route for synthesizing many types of isomorphous forms of zeolites at certain Si/M ratios (M=Al, Ga, Ti, etc.), which offer opportunities for synthesizing heteroatom-substituted metallosilicate zeolites, where the metal ions might otherwise be difficult to incorporate into the framework during direct synthesis (Chen, C. Y.; Zones, S. I. In 13th International Zeolite Conference; Galarneau, A., Di Renzo, F., Fujula, F., Vedrine, J., Eds.; Elsevier: Amsterdam, 2001, p paper 11.) In such a modification of one framework metal for another, the B atoms templates certain T-positions in the zeolitic framework, and silanol nests can be created upon deboronation (Deruiter, R.; Kentgens, A. P. M.; Grootendorst, J.; Jansen, J. C.; Vanbekkum, H. Zeolites 1993, 13, 128; and Hwang, S. J.; Chen, C. Y.; Zones, S. I. Journal of Physical Chemistry B 2004, 108, 18535.) Such silanol nests can be re-occupied via tetrahedral molecular recognition by another metal ion, which has a size and oxygen coordination geometry similar to B in the framework, which favors formation of tetrahedral MO4 sites. It has been discovered that treatment of borosilicate zeolites with Al(NO3)3 solution in a single step successfully exchanges B sites in 12-membered rings (12MR) or on the external surface with Al sites. The resulting sites exhibit strong Brønsted acidity. However, it has also been demonstrated heretofore that it is not possible to exchange B sites that are located in 10 MR, presumably due to the bulkiness of Al(H2O)63+ hydrated cations.
Zeolite catalysts, in general, consisting of microporous crystalline aluminosilicates, are widely used in petroleum refining and fine-chemical synthesis because their strong acid sites within uniform micropores give both high activities and shape selectivities. However, their applications are limited to small-molecule synthesis due to small aperture size (<2 nm) of micropores. Delaminated zeolites are very desirable due to their high accessibility for bulky molecules, but typically require expensive organic surfactants to affect delamination. Other large-molecule accessible zeolites include extra-large pore zeolites, single-unit-cell zeolite nanosheets, hierachically nanoporous zeolitelike materials, and self-pillared zeolite nanosheets, but all require surfactants for synthesis.
Of value to the industry would be a suitable synthesis which is simple and more economical, e.g., not requiring the use of a surfactant.